Abstract

The inorganic nitrogen cycle (Fig. 1) consists of several linked biological processes and one abiological process, the reaction of N2 and O2 in lightning discharges (and internal combustion engines) to produce NOx and, ultimately, nitrate. All of the processes except nitrogen fixation involve reduction or oxidation of species containing N-O bonds of order greater than one, such as NO−3, NO−2, NO, and N2O. Except for the assimilatory reduction of nitrite to ammonium, which is a complex six-electron process that is unique in nitrogen biochemistry, the reactions of inorganic N-oxides are of potential interest as relatively well-studied paradigms that may be relevant to aspects of biological degradation of nitroaromatic compounds. One might expect the existence of analogous chemistry in the reduction of NO−2 or HNO2 and ArNO2 (where Ar is a general abbreviation for an aromatic group). Certainly both the inorganic and organic species contain nitrogen in the same oxidation state (+ 3), and they also contain two N-O bonds that possess at least partial multiple bond character.